1. Field of the Invention
The present invention relates to a material to be used for an antireflection film to be formed on a workpiece disposed on a semiconductor substrate and a method of manufacturing a semiconductor device using the same material, particularly to a material for forming an antireflection film to be prepared directly under a photoresist film to improve the processing accuracy of the photoresist.
2. Description of the Related Art
In case of the resist patterning through light exposure, the resist pattern has often suffered from a disfigurement (notching) caused by light reflected from a different level part of the substrate or suffered from the dimensional variation of the resist pattern induced by the thickness fluctuation of the resist film. For solving the above problem, there is proposed a method which forms an antireflection film directly under a resist film for preventing the reflection of exposure light, thereby decreasing the reflection light from the substrate. This antireflection film is divided into two types, one is an organic film formed by spin coating applied on a workpiece as is the case with a resist, the other is an inorganic film formed by a CVD (Chemical Vapor Deposition) method. These methods have the following features, respectively.
The inorganic antireflection film can be formed to the fixed thickness irrespective of the difference in the surface level of the workpiece, and hence it is possible to decrease the dry etching time and reduce the dimension conversion difference between the resist and the antireflection film, the dimensional variation of the resist pattern is generated due to a resist thickness change caused by the existing surface level difference.
The organic antireflection film can be formed by coating a material in the same way as the resist film, and hence it has a tendency that the surface level difference of the substrate can be flattened, and accordingly the film tends to have the uniform thickness without being affected by the existence of the surface level difference, thereby allowing to control the dimensional variation due to the fluctuation of the thickness of the resist film. The organic antireflection film is produced by adding an ultraviolet light absorber to the resin material (such as polyimide) which generally constitutes a base.
The technique concerning the coating type antireflection film of this kind has been known to the public, being disclosed in a monthly "Semiconductor World", July, 1995. pp. 100-102 for, example.
FIG. 1A to FIG. 1E are sectional views each showing, in the process order, a manufacturing method of the conventional semiconductor device which utilizes a coating type antireflection film. As shown in FIG. 1A, workpiece 32 is first formed on semiconductor substrate 31, then successively coating type antireflection film 33 is formed, and photoresist film 34 is formed on antireflection film 33. The photoresist 34 is selectively exposed through an exposure mask to the exposure light, such as infrared radiation or a KrF excimer laser beam, and as shown in FIG. 1B, developed to form resist film pattern 34a of etching-proof property. Next, as shown in FIG. 1C, dry etching operation is selectively applied to antireflection film 33 using resist film pattern 34a as a mask to form antireflection film pattern 33a. Through this process, the film thickness of resist film pattern 34a is reduced, being concurrently etched. Then, as shown in FIG. 1D, by using this etching-proof resist film pattern 34a and antireflection film pattern 33a as a mask, workpiece 32 is selectively etched to form workpiece pattern 32a. Next, as shown in FIG. 1E, by using oxygen (O.sub.2) plasma, residual resist film pattern 34a and antireflection film pattern 33a are removed through ashing, thereby obtaining a desired workpiece pattern 32a.
Under the present conditions, the dry etching selectivity of the photoresist is not sufficiently high against the antireflection film. Therefore, as shown in FIG. 2A, when antireflection film 33 and resist film pattern 34a are formed on workpiece 32 which has a large difference in the surface level and the antireflection film is etched using resist film pattern 34a as the mask, at the processing stage that the antireflection film etching is completed in the concave portion having a thick film, as shown in FIG. 2B, the residual film of resist film pattern 34a has become unable to secure a sufficient film thickness. As a result, as shown in FIG. 2C, when dry etching workpiece 32, resist film pattern 34a vanishes and further antireflection film pattern 33a partially disappears. Consequently, as shown in FIG. 2D, the pattern of the workpiece is deformed when the patterning of workpiece 32 is completed.
Therefore, a problem to be solved by the present invention is to prepare a method such that a photoresist film can secure the sufficient etching selectivity against the antireflection film, the reduction in film thickness of the photoresist film can be controlled when the antireflection film patterning is executed, and accordingly the workpiece patterning can accurately be performed.